Mr. Rosenberg, who was appointed by President Barack Obama in 2015, is a career prosecutor. Under President George W. Bush, he served as the United States attorney in both southern Texas and eastern Virginia.

DEA officials say Sessions and his Justice Department have pressed the agency for action specifically on MS-13 despite warnings from Rosenberg and others at the DEA that the gang, which draws Central American teenagers for most of its recruits, is not one of the biggest players when it comes to distributing and selling narcotics.

Mexican cartels, DEA officials have warned, will use any gang to sell their drugs, and DEA leaders have directed those in their field offices to focus on the biggest threat in their particular geographic area. In many parts of the country, MS-13 simply does not pose a major criminal or drug-dealing threat compared with other groups, these officials said.